/bhavatR- / भवतृॱ

The base "bhavatR-" "who is" comes from **bhava- भवॱ + /zatR.

When masculine, like all atR अतृ bases, it takes the endings the same way as /matup bases like /bhavatu- and "hanumatup". The exception is the /su that is not the /sambuddhi, which does not cause lengthening —

/bhavatR- + /su → **bhavan भवन् like **hasan हसन्

/bhavatR- + /am → **bhavantam' भवन्तम्ऽ like **hanumantam हनुमन्तम्

While it does cause lengtheninng of the /udit —

/bhavatu- + /su → **bhavAn भवान् like **hanumAn हनुमान्

bhavatR- भवतृॱ + /bhis → !**bhavadbhis' भवद्भिस्ऽ "by the ones who are"

bhavatR- भवतृॱ + /zas → !**bhavatas' भवतस्ऽ " o who are"