Help!!!!! Advice needed

So my pup of 10 months got castrated about 3 weeks ago (6th Sept) my new puppy bitch 4 months came into her 1st heat Friday just gone.... done my best to keep them busy and apart. . But you know what I'm going to say... he got her. . Caught them too late and they locked on.. 😧🙈 have no idea what to do.. obviously I'll call the vets in the morning. What's people opinion on chances of pregnancy?