How to pass data from one usercontrol to another usercontrol

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ASP.NET

i have two usercontrols like below in service.aspx file

<%@ Register Src="BPRS.ascx" TagName="BPRS" TagPrefix="ucBPRS" %>
<%@ Register Src="MMSE.ascx" TagName="MMSE" TagPrefix="ucMMSE" %>

as per current implementation

1.enter clientId in BPRS will auto populate other details in BPRS.

2.handling everything in same user control

but I need to do

1.enter clientID in BPRS should auto populate details in BPRS(get by ClientID related details) and MMSE(get by ClientID related details).

2.simplity when i enter clientId in BPRS ,it should hit MMSE usercontrol as well .

Is there any way to do this ? I was unable to find in my search .

What I have tried:

i tried

MMSEx = new MMSE();

in

BPRS

but it through null error .