You should talk to Goldmali, who took on a rescue Malinois, who turned out to be pregnant.
Only canine male she had been with was a Chihuahua!!!Yes that really was the surprise of a lifetime! Rescue bitch who came to us as her fourth home within a month, she looked a little bit podgy but she was so stressed out that the vet simply could not examine her properly, but she figured she probably wasn't pregnant, most likely having a phantom. A couple of weeks later the bitch had settled next to me on the couch one evening and as I was stroking her sides, I felt puppy movement. We contacted the original owner which was the only one she could have got pregnant whilst with due to the timings involved, and was told "But we only have one other dog and he is a Chihuahua". (Interestingly she gets on much better with little dogs than ones her own size.)
22 days after she arrived she whelped 4 pups. They looked very similar to Malinois pups, but not quite, and amazingly they were more or less the same size/weight that you would expect newborn Mali pups to be. Then life became rather difficult as the poor bitch, who had trusted me enough to stay with her whilst she whelped, decided she wanted nobody near her pups. Not me, not my husband -she even went mad when birds flew past the window. She was being extremely aggressive and totally stressed out. Can't blame her at all but it was quite scary. It took 2 weeks before I could as much as look at the pups whilst she was in the same room. By 5 weeks she had settled and was happy to let anyone see the pups.
As the pups grew it became more and more obvious that they had Chihuahua looks. Zero doubt. Even Chihuahua breeders said so. I rehomed two to previous Malinois puppy buyers, and one to an experienced friend of a friend. There was no way I was going to advertise these pups for sale to strangers so we simply kept the last pup left.
These pups are now 2 ½ years old. They all look very similar; two are red sable, two are fawn sable, and the one dog is a bit bigger than the bitches. They are around 12 inches tall. Essentially they look like badly bred over sized Chihuahuas. Not all that different from many dogs sold as Chihuahuas! But they are 100 % WORKING line Malinois in temperament, and believe me, that means they are NOT ever going to be pet dogs. The energy levels are sky high. I hope nobody ever does the cross deliberately as it would be a disaster! If we hadn't seen them be born, you'd never believe they came from the mother they did as their looks are all from their father.